Marijuana has long been considered to have a substantial effect on human sexual behavior. However, there has been very little research that objectively evaluated this effect without resorting to verbal reports and/or subjective interpretations of personal experience. This research shall objectively evaluate the effects of marijuana (1) on sexual arousal, as elicited by visual stimuli and measured by penile erection using the method of Laws and Rubin (1969); (2) on the ability to inhibit and/or enhance elicited sexual arousal; (3) on the ability to become sexually aroused by fantasy; and (4) on the blood plasma levels of testosterone, FSH and LH (to determine if marijuana inhalation results in concurrent changes in sexual arousal and sex hormonal levels that would be indicative of the drug's mechanism of action on arousal). Data evaluation shall include dose-response curves on latencies, intensities and patterns of responding. The research will not only provide objective information about the effects of marijuana on sexual responding, but also develop a procedure of evaluating the effects of other drugs on sexual behavior.